In a non-aqueous electrolyte secondary battery, when an internal short circuit occurs, it causes a large current in the battery, and as a result sometimes elevates the temperature inside the battery. This temperature elevation may induce a reaction between the positive electrode active material and the non-aqueous electrolytic solution. In particular, an internal short circuit due to a stress applied from the outside to a battery in a fully charged state discharges a large energy almost instantaneously to elevate the battery temperature, and this temperature elevation induces the reaction between the positive electrode active material and the non-aqueous electrolytic solution. If this reaction cannot be suppressed, the rapid elevation of the temperature is likely to occur.
Here, examples of the cause for an internal short circuit include penetration with an object having a sharp tip (e.g., a nail), the collapse of a battery due to crushing, and an impact due to falling. In the case of an internal short circuit due to penetration with a sharp object, a large amount of Joule heat is generated near the collector, and the heat induces the reaction between the positive electrode active material and the non-aqueous electrolytic solution, which is likely to cause the rapid elevation of the battery temperature. In Patent Literature 1, it is disclosed to suppress the reaction between the positive electrode active material and the non-aqueous electrolytic solution by blending a solid flame retardant agent in the positive electrode mixture or the negative electrode mixture. Further, in Patent Literature 2, it is disclosed to suppress the combustion of the battery-constituting materials by disposing a flame retardant agent layer containing a flame retardant agent on either surface of the positive electrode, the negative electrode or the separator.